Rare frog that breeds inside hollow stem of bamboo

New Delhi: The white spotted bush frog, thought to be extinct for over a century until re-discovered a few years ago, has a peculiar reproductive habit, it lays eggs and hatches them inside hollow stem of bamboo.

This hitherto unknown behavior was documented in the remote Kalakad Mundanthurai Tiger Reserve in the Western Ghats by Seshadri K S, a PhD student at National University of Singapore; his thesis advisor David Bickford and collaborator Gururaja K V from the Indian Institute of Science, Bangalore, says a Gubbi Labs release.

The frog enters hollow, living bamboo stems via small openings and deposits eggs, which hatch directly into froglets. Adult frogs then stay with the eggs and young froglets, providing parental care.

The white spotted bush frog (Raorchestes chalazodes) is green in colour and less than three cm in length. It belongs to the diverse group of 'tree frogs', (Rhacophoridae; Raorchestes).

It was thought to be extinct for over a century until it was re-discovered a few years ago by a team of scientists working in the remote Kalakad Mundanthurai Tiger Reserve.

It is currently listed as 'Critically Endangered' by the International Union on Conservation of Nature and Natural Resources (IUCN).

Adult males start vocalizing early in the evening and they enter bamboo via a small opening, which is usually less than 5-10 mm long and 3-4 mm wide.

They continue to call from inside the bamboo. The female follows the male inside and then lays 6-7 eggs inside. These eggs directly develop into froglets; there is no tadpole stage in these frogs.

The male stays inside the bamboo, taking care of the eggs. Other females may choose to mate with the male, and deposit 5-8 eggs on their own. The eggs are few in number but are quite large for such a small frog, measuring an average of 5 mm in diameter.

"We had heard frogs calling from inside bamboo and one night went in search of them. On seeing a frog vocalising on a bamboo leaf, we began making observations and the frog squeezed itself into a narrow opening nearby," said Seshadri.

"Several night searches later, we were able to observe eggs and froglets inside bamboo by carefully splitting it open. However, this discovery is just the beginning. It has opened a whole new world of questions that are waiting to be answered. As to what transpires inside the internode, it's still a mystery," he added.

This behavior is an addition to the diverse means in which amphibians reproduce and is classified as the 41st mode in all frogs.

Direct developing eggs are perhaps the most striking aspects of frogs as they do not require any free flowing water to develop.

The Western Ghats hotspot is known to be an important site for amphibian radiation and several novelties have been uncovered in the last two decades. While species diversity has increased, very little ecological information has been added.

"The recent discoveries of interesting behavior such as Foot Flagging in the Dancing frog and clay nest building in Potter frog are cases which indicate that there is much more to be discovered about amphibian behaviour in India and S E Asia," said Gururaja K V.

"This is a significant discovery in two ways, first, it reiterates that natural history observations are fundamental for understanding evolutionary ecology and second, it sets a theoretical foundation to ask several interesting questions about the diversity of reproductive modes and the evolutionary pathways behind such amazing amphibian behaviour," said Bickford.